Thermal-Mechanical Characterization/Selection of a Two-Part Epoxy Cure
Profile for Structural Bonding
Zach Hollcraft, Cham Hang Yeung, Talia Vyeson, Adriano Liao, Seniors, Anthony Bou, Mechanical Engineering
Dr. John Bridge, Assoc Prof, Mechanical Engineering, Sponsored by Collins Aerospace
Description Design Constraints:
An off-the-shelf two-part thermoset epoxy, used for
structural bonding of commercial jet aircraft interiors,
was tested and analyzed to find improved cure profiles
over manufacturer-supplied cure specifications. Testing
methods include tensile testing, differential scanning
calorimetry (DSC), thermogravimetric analysis (TGA).
Additionally, fracture surfaces were analyzed via stereo-
microscopy and scanning electron microscope to confirm
cures failed.
Tensile Testing:
Mechanical lap-shear
tensile testing on all cure
profiles provided average
and peak shear strengths
for the epoxy:
Scanning Electron Microscope (SEM):
Future Experiments/Discussion:
Additional cure profiles should be considered at a wider
range of temperatures and cure times. Also, additional
DSC testing on proposed cures would provide useful
information on cure characteristics.
Sample Preparation:
Pre-cut and treated aluminum
plates are used as the bond
surface for lap-shear testing.
A jig was designed using CAD to
align and clamp the tensile test
sample plates while curing to
ensure a complete bond.
Contact:
keith.anderson2@collins.com, hollczac@uw.edu, bouda@uw.edu,
liaoa3@uw.edu, tnvyeson@uw.edu, chyeung@uw.edu
Thermogravimetric Analysis (TGA):
Two samples with the same 1 hour cure profile were
tested. Both samples quickly began to degrade at about
300℃. This gives a temperature limit for DSC testing.
Epoxy sample completely
pyrolyzed and left behind
ash by 750℃
Stereo-Microscope:
Air bubbles occur due to the preparation process
The 1 hour cure samples have a rougher surface
The 5 day cure samples have a smooth surface
Scratches are caused by MTS testing or samples handling
after the tests
The 1 hour (250ºF) epoxy sample
Left: Edge of the shearing surface
Right: Shearing surface
The 5 days (room-temperature) epoxy sample
Left: Edge of the shearing surface
Right: Shearing surface
SEM pictures of the 5-day room temperature
cure. Sample fracture surface was observed
to analyze fracture geometry and look for
possible contaminants or air bubbles.
Goal Problem Statement:
To develop an improved set of cure profiles for a two-
part epoxy Loctite Hysol EA9309.3NA over
the manufacturer's recommended cures.
Conclusion:
Mechanical testing provided data to support the 1-hour
@ 250°F cure as having the highest average peak break
strength. Additional testing of planned cure profiles, and
DSC testing, would have supplied important statistics to
determine optimal cure profiles for different situations.
Stress vs strain plot of 1hr @ 250F
CAD assembly of jigCutting samples from cured plate
3 different sample plates before curing
Cure
Profile
Constant
Area (in²)
Avg Peak
Load (lbf)
Standard
Deviation
Avg
Peak Stress
(lbf/in²)
Standard
Deviation
5 day
(72 F)
0.601
2216.37
24.628
3690.27
41.006
2 hr
(180 F)
0.601
2177.10
175.253
3873.40
313.021
1
hr
30 min
(226 F)
0.601
2192.44
52.736
3901.14
93.836
1
hr
15 min
(226 F)
0.601
2210.237
36.09
3931.81
64.463
1 hr
(250 F)
0.601
2450.171
49.257
4079.539
82.012